The lamprey brain stem and spinal cord offer many of the experimental advantages of invertebrate preparations: survival in isolation, visibility of large cells and axons, relative simplicity, and the ability of single neurons to elicit movements. At least three groups of interneurons, three kinds of motoneurons, one group of conspicuous sensory cells, and perhaps twenty individual reticulospinal neurons have been identified morphologically and physiologically. One goal of this project is the determination of functional interconnections of identified cells using simultaneous intracellular stimulation and recording, and the correlation of the activities of these cells with simple reflexes and simple components of behavior. A second goal is the physiological, morphological, and chemical study of large identified synapses in the spinal cord.